Does anyone have any info on this issue? 

For long guns in the state of Hawaii, the barrel must be at least 16 inches long. The muzzle device would have to be pinned and welded to the barrel to make the overall length 16 inches. With it welded to the barrel, it becomes part of the barrel. Therefore not falling into the SBR category, which you can't legally have in this state. I have a few rifles with 14.5" barrels pinned and welded to 16". There are extended flash hiders and muzzle brakes specifically made for this, like BCM's A2X flash hider. It's .5" longer to achieve the 16" requirement when attached to a 14.5" barrel.

The device needs to be permanently attached to the end of the barrel (eg pinned and welded), and the overall length of barrel plus device is greater than 16"

Permanent methods of
attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver
soldering, or blind pinning with the pin head welded over. Barrels are measured by inserting a dowel rod
into the barrel until the rod stops against the bolt or breech-face. The rod is then marked at the
furthermost end of the barrel or permanently attached muzzle device, withdrawn from the barrel, and
measured.
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https://www.atf.gov/firearms/docs/atf-national-firearms-act-handbook-chapter-2/download

Right on much mahaloz for the info guys!!!!